The present invention is related to an electrode for destruction of biological tissue, suitably tumour tissue such as cancer. The tip, or head, of the electrode is substantially spherical in order to obtain a symmetrical circular destruction zone.
One way of treatment of biological tissue is electrochemical treatment of cancer (ECT), which is a rather undeveloped method to eliminate biological tissue. Greater understanding of the mechanisms of electrochemical treatment is needed for the method to get recognised. The development of ECT as a clinically acceptable therapy has been hindered by uncertainties regarding the mechanism of tissue destruction and the parameters that are important in the process. To be able to understand the mechanism behind ECT, and to develop an effective dosage method, a Swedish interdisciplinary research group, was formed in 1993.
In electrochemical treatment of cancer (ECT), the biological tissue is treated with a direct current. The anode is preferably placed in the biological tissue and the cathode is placed in a blood vessel or in fresh surrounding tissue. When using platinum electrodes, the main reactions are decomposition of water along with oxidation and reduction of substances dissolved in tissue. Consequently, the evolution of oxygen, as well as acidification and formation of chlorine, take place at the anode: EQU 2H.sub.2 O.revreaction.O.sub.2 +4H.sup.+ +4e.sup.- (1) EQU 2Cl.sup.- .revreaction.Cl.sub.2 +2e.sup.- (2)
At the cathode, water is decomposed into hydrogen and hydroxyl ions: EQU 2H.sub.2 O+2e.sup.- .revreaction.H.sub.2 +2OH.sup.- (3)
The ionic species produced at the anode and cathode are transported to the surrounding tissue, mainly by means of diffusion and migration. pH values down to 1 are usually obtained in the tissue close to the anode and a pH of about 12 can be measured at the cathode. Due to the formation of acid and base hematin, the affected tissue becomes dark brown. During electrolysis, the current density may usually be about 10.sup.-2 -10.sup.-1 A/cm.sup.2 and the voltage between the anode and cathode can be about 5-15 V. The toxic and destroying action of ECT is assumed to be due to a strong acidification of a zone around the anode, chlorination of tissue constituents close to the anode, electrocoagulation and other possible effects caused by the electric field.
The relatively high current density used for ECT-electrodes, is a prerequisite in order to maintain the oxygen evolution and the acidification around the anode. For this reason, the electrode material and geometry are crucial elements in ECT treatment. For instance, electrodes made of stainless steel would not be suitable for maintaining the oxygen evolution and the acidification around the anode. With respect to the geometry, a needle shaped and tapered head of the electrode causes a non-uniform current distribution, resulting in a oval and unpredictable destruction zone in the tissue.
Endocardiac electrodes, constructed for stimulation of the heart or other muscles, cannot be used for destruction of biological tissue. Endocardiac electrodes uses pulsed current with a low current density. Initially, the current density can be about 10.sup.-3 A/cm.sup.2, but is quickly transferred to about 10.sup.-5 A/cm.sup.2. If the purpose of the endocardial treatment is just to gently stimulate nerves of a certain type of tissue, the current density will be as low as in the range of 10.sup.-5 A/cm.sup.2 down to 10.sup.-7 A/cm.sup.2. Besides, the shape and the material of endocardiac electrodes are different compared to electrodes for biological tissue destruction. Moreover, mechanical stability of wire electrodes is often poor due to the tapered end and the overall construction, which implies that wire electrodes only can be used a few times.
U.S. Pat. No. 4,677,990 relates to an endocardial electrode having a flexible electrical conductor, which can assume arbitrary curvatures or contours.
EP-B1-0038484 discloses an endocardial electrode arrangement for the intracardial stimulation of the heart. The electrode comprises a plurality of loops of soft material and are fastened to the electrode head. The aim is to fix electrode to the heart wall.
EP-A-316995 relates to an electrode for treatment of body tissue. The electrode is formed by a platinum wire which is passed through a tube of insulating material. The head of the electrode is formed by winding the end of the wire.
The aim with the ECT treatment is to get a uniform, symmetrical and reproducible destruction zone. This aim is met by the electrode of the present invention.
According to the present invention, the above mentioned problems have been solved by providing an electrode for destruction of biological tissue, comprising an electrical conductor with a first thickness, provided with electrical insulation having a second thickness, the conductor being connected to a current source at one end and electrically connected to an electrode head at the other end of the conductor, where the electrode head serves for supplying current to the zone of the biological tissue, wherein the electrode head is substantially spherical with a diameter, where said diameter of the sphere is equal to or larger than said first thickness.
The advantage with the electrode of the present invention is above all the creation of a substantially symmetrical circular destruction zone. This is due to the possibility to create a uniform current distribution with the spherical head of the electrode according to the present invention. One great advantage is the predictability of the destruction area. Further, the mechanical stability of the present new electrode is superior to conventional electrodes and this allows for the electrode to be used in many treatments before it has to be discarded. Besides, this new construction of electrodes opens the possibility for a wide range of applicable embodiments.